Aspartame, an artificial sweetener, has recently received some attention in the news! This followed the World Health Organisation classifying aspartame as a “possible carcinogenic substance”. Immediately, social media and the news blew up with messages that aspartame causes cancer. Afterall, it is the WHO, and they know best. But it is not the WHO that is the problem. Instead, it is the human brain that wants a simple answer to the question “does aspartame cause cancer?”. The WHO concluded that aspartame is a “possible” carcinogenic substance… they did not conclude it is, and they did not conclude it isn’t. As always, the answer is more complicated than yes or no. So, lets clarify the evidence around aspartame and cancer.
What is aspartame?
Aspartame is a sweetener we find in many diet sodas. Many people drink several cans a day. So, the question of whether it is carcinogenic is obviously an important one. However, it is not the only question we should look at. We should also look at questions like: what is the evidence? Where does the evidence come from? How strong is it? And we should also look at questions like are there other effects of aspartame? Positive or negative.
Does aspartame cause cancer?
The WHO listed aspartame as a “possible” carcinogenic substance. Aspartame ended up in the in Group 2B. It joins a number of other compounds with the tag a possible carcinogen with “far from conclusive” evidence. Anyone who claims that WHO classified aspartame as a carcinogen clearly hasn’t read the WHO report and is plainly wrong. “Possible” and “definite” are not the same.
If there had been more evidence to support aspartame as a carcinogen, it would have been ended up in group A where we find asbestos and also processed meats (a discussion for another day). Group 2A are probable carcinogens like acrylamide and unprocessed red meats. Group 2B are possible carcinogens and include things like aloe vera and pickled vegetables. For the full list, visit: https://monographs.iarc.who.int/list-of-classifications
Should we stop drinking soda with aspartame?
One study that triggered the WHO to look at the evidence was published in 2022 (1). This rare study in humans found a 15% greater risk of developing cancer. However, this was a cohort study which can only provide weak evidence. It is also often ignored that this study cannot provide any information about causality. There is no evidence that aspartame caused the cancer. There are many ways in which aspartame users can be different from non-aspartame users. People that avoid aspartame may be more aware of what they consume and make a host of other nutrition choices, aspartame users are often people that diet, have weight fluctuations and may have different exercise behaviours. There are many reasons why aspartame users would have a higher risk, the use of aspartame is only one of those reasons.
A recent study found a 15% higher risk of developing cancer, but this could be caused by many factors
There are also no dose response studies. If aspartame causes cancer, you would expect that more aspartame increases the risk and this is something that research hasn’t shown. Almost all evidence on aspartame is from animal studies and in these studies mega doses of aspartame were used. It is really not clear how these studies translate to humans especially when doses are used that are within the range that is normally consumed.
Most governing bodies and research studies use a safe upper limit for aspartame of about 17-18 cans of soda a day for a 75kg person. There may be individuals that on occasion reach that level, but there will not be many who drink that much diet soda, and if they do they will unlikely be doing this on a daily basis for many years in a row.
So, can we conclude that aspartame is carcinogenic? No. Can we conclude that it is not carcinogenic? No. We can conclude that the evidence that aspartame, in doses that are normally used, is carcinogenic in humans is very weak. Should we stop drinking soda with aspartame? Probably not, especially if it helps to replace sugar containing beverages and this helps you to control body weight. By removing aspartame and introducing sugar it is possible that you cause more problems than you solve. If worried about aspartame, you can also reduce its intake by using other non-caloric sweeteners as well. Unlike the animals in animal studies, we have a choice; we can decide how much aspartame and which other sweeteners we use.
Debras C, Chazelas E, Sellem L, Porcher R, Druesne-Pecollo N, Esseddik Y, de Edelenyi FS, Agaësse C, De Sa A, Lutchia R, Fezeu LK, Julia C, Kesse-Guyot E, Allès B, Galan P, Hercberg S, Deschasaux-Tanguy M, Huybrechts I, Srour B, Touvier M. Artificial sweeteners and risk of cardiovascular diseases: results from the prospective NutriNet-Santé cohort. BMJ. 2022 Sep 7;378:e071204. doi: 10.1136/bmj-2022-071204. PMID: 36638072; PMCID: PMC9449855.